The lightcurve of a Mira shows regular, long period (from several months to
longer than a year) and large amplitude (from a few to \(>\) 10 magnitudes)
sinusoid-like variations (e.g.
[1]}, [2]}). The large scale radial
pulsation is betrayed by the in-phase variation of the radial velocity of
the absorption spectrum, with amplitudes of the order of \(\sim \) 10-15 km/s
[3]}, [1]}. Our path-finder SU Lyn
shows a significant variability (0.6 mag amplitude in \(V\) ), but it lacks the
larger amplitude and the regular beat of a Mira. As clearly illustrated by
Fig. REF , the M giant in SU Lyn does not radially pulsate
in any significant way (the absorption lines are stable in radial velocity
to better than 2 km s\(^{-1}\) ), and therefore no shocks form in the
atmosphere which could lead to emission in the Balmer lines. Armed with
these considerations, and to stay on the cautionary side, we selected to
flag (in the 83-sample) all the stars showing ASAS-SN lightcurves with an
amplitude in excess of 0.7 mag and a stable and clean sinusoid-like shape
(cf. Fig. REF ). Such a lightcurve could however arise
also from orbital motion, for example from ellipsoidal distortion when the
cool giant fills its Roche lobe and/or its side facing the companion is
irradiated and heated up (e.g. as in the accreting-only and recurrent nova
T CrB; [5]}). A spectroscopic confirmation of the
radially pulsating nature is therefore required, and this needs to be
accommodated within the single-epoch spectra (i.e. no revisit) of the GALAH
survey.
